Is it possible to access just part of a data path with Python?
The script below gets the data path, converts it to a string. Then does the manipulation on it to get the desired part. 

I split the string on "sequence_editor." because everything after that (except for the closing bracket) is what you want, a period would also work.

After splitting the string (string[-1]) that line gets the last item in the list.
Using your data path the list would look like this: 

["[bpy.data.scenes['Scene'].", 'sequences_all["Image0001.png"]]']


The last item in the list sequences_all["Image0001.png"]] only needs to have the trailing bracket removed (last line of the script.)

import bpy

path = bpy.context.selected_sequences
string = str(path) #convert data path to string
string = string.split("sequence_editor.") #split string in to a list
string = string[-1] # get last piece
string = string[:-1] # remove last character
print(string)


Your problem was you were trying to get the first part of the path x = n[0] before turning it in to a string and then splitting it into a list.